. >> really a beautiful way to look back at his life, john carlin, thanks so much. in our next half hour president obama's tribute to nelson mandela during a lighting of the national christmas tree and wyntoon marsalis. >>> chuck hagen made a surprise visit to u.s. troops in afghanistan. reassureing alleys. a clear-eyed real and difficult engagement. underscoring how difficult it is hagel toured a u.s. navy ship keeping watch off iran. margaret brennan has more. >> reporter: defense secretary chuck hagel climbed aboard a ship with a message -- a diplomatic breakthrough with iran doesn't change the threat level in the region or the u.s. military presence. >> this region is is dangerous. it's combustible. it's unstable. but having a steady american hand in this region to help our allies and reassure our allies is really key. >> reporter: the ussponce is part of the nave fleet which defends american assets. this ship is the pentagon's first command and staging base in the persian gulf. it's 120 miles off the coast of iran and it's outfitted with small drone aircraft un